VARIANCE ANALYSIS OF IMMUNOGLOBULIN ALLELES IN NATURAL-POPULATIONS OFRABBIT (ORYCTOLAGUS-CUNICULUS) - THE EXTENSIVE INTERALLELIC DIVERGENCE AT THE B-LOCUS COULD BE THE OUTCOME OF OVERDOMINANCE-TYPE SELECTION

Population genetic data are presented which should contribute to evalu ation of the hypothesis that the extraordinary evolutionary patterns o bserved at the b locus of the rabbit immunoglobulin light chain consta nt region can be the outcome of overdominance-type selection. The anal ysis of allele correlations in natural populations revealed an excess of heterozygotes of about 10% at the b locus while heterozygote excess was not observed at loci determining the immunoglobulin heavy chain. Data from the published literature, where homozygote advantage was sug gested, were reevaluated and found in agreement with data here present ed. Gene diversity was evenly distributed among populations and showed similarities with patterns reported for histocompatibility loci. Anal ysis of genotypic disequilibria revealed strong digenic associations b etween the leading alleles of heavy and light chain constant region lo ci in conjunction with trigenic disequilibria corresponding to a prefe rential association of b locus heterozygosity with the predominant all ele of the heavy chain e locus. It is argued that this may indicate co mpensatory or nonadditive aspects of a putative heterozygosity enhanci ng mechanism, implying that effects at the light chain might be more p ronounced in populations fixed for the heavy chain polymorphism.